Two internal systems interact to regulate when we sleep and when we are awake. These systems are the sleep/wake homeostat, which monitors our need for sleep based on how long we have been awake; and the circadian system, which regulates the cycling of numerous functions, including when we sleep and wake, every 24 hours.

These two systems usually counterbalance each other. However, because they operate independently, they can become misaligned. Irregular schedules and jet lag wreak havoc with these highly synchronized systems that regulate sleep and wake under normal conditions. During jet lag or shift work, for instance, we might experience an alerting signal when trying to sleep, or, conversely, a powerful drive to sleep when we need to be awake.

Take a tour of these systems, and then explore factors that disrupt their normal interaction.